If anyone doubted what kind of Iraq has been bequeathed by a decade of US-sponsored occupation and war, today's deadly sectarian bomb attacks around Baghdad against bus queues and markets should have set them straight. Ten years to the day after American and British troops launched an unprovoked attack on a false pretext – and more than a year since the last combat troops were withdrawn – the conflict they unleashed shows no sign of winding down.

Civilians are still being killed at a rate of at least 4,000 a year, and police at about 1,000. As in the days when US and British forces directly ran the country, torture is rampant, thousands are imprisoned without trial, and disappearances and state killings are routine.

Meanwhile power and sewage systems barely function, more than a third of adults are unemployed, state corruption has become an institutionalised kleptocracy and trade unionists are tried for calling strikes and demonstrations (the oil workers' leader is in court in Basra on that charge tomorrow). In recent months, mass protests in Sunni areas have threatened to tip over into violence, or even renewed civil war.

Whether either is ever held to account for it, global opinion against the Iraq war is long settled – including in Britain, the US and Iraq. The invasion was a flagrant act of aggression against a broken-backed state, regarded as illegal by the overwhelming weight of international legal opinion.

The onslaught triggered a death toll which certainly runs into hundreds, rather than tens, of thousands: estimates range from the Iraq Body Count's minimum of 173,271 up to 2012 (acknowledged to be an underestimate) through the Iraqi government and World Health Organisation's 223,000 and Lancet survey's 654,965 "excess deaths" in the first three years, to the ORB polling organisation's estimate of more than a million.

The occupation was a catastrophe for Iraqis. It destroyed the country's infrastructure, created 4 million refugees, reduced cities like Falluja to ruins – littered with depleted uranium and white phosphorus as cancer rates and birth defects multiplied – and brought al-Qaida and its sectarian terror into the country.

That wasn't the result of mistakes and lack of planning, as the US and British elites like to tell themselves. But as with the armed resistance that mushroomed in the aftermath of the invasion, they were foreseeable and foreseen outcomes of what by any sober reckoning has been a reckless crime.

Saddam Hussein "created enormous carnage", Blair said today – which was certainly true in the years when his regime was backed by Britain and the US. But that is exactly what Bush and he did in their war to overthrow him. The biggest improvement in Iraqis' lives thereafter came as a result of the lifting of US and British-enforced sanctions, estimated by Unicef to have killed half a million Iraqi children in the 1990s.

Ten years on, the US still has a powerful presence in Iraq – now starting to resemble a sort of American-Iranian condominium – with thousands of military contractors, security and intelligence leverage and long-term oil contracts. But it's a long way from the archipelago of bases and control its leaders had in mind.

Iraqi success in preventing a permanent occupation is down to resistance, armed and civil, Sunni and Shia. But that achievement was undermined by the eruption of sectarianism in the aftermath of the invasion, fostered by the occupying forces in the classic imperial divide and rule mould.

One outcome is the authoritarian Shia elite-dominated state run by Nouri al-Maliki today. His Sunni vice-president until last year, Tariq al-Hashimi – forced to leave the country and sentenced to death in absentia for allegedly ordering killings – was one of those who in his own words "collaborated" with the occupation, encouraging former resistance leaders to join Petraeus's "awakening councils", and now bitterly regrets it. "If I knew the result would be like this, I would never have done it," he told me at the weekend. "I made a grave mistake."

The sectarian virus incubated in the occupation has now spread beyond Iraq's borders and threatens the future of states across the eastern Arab world. But the war hasn't only been a disaster for Iraq and the region. By demonstrating the limits of US power and its inability to impose its will on peoples prepared to fight back, Iraq proved a strategic defeat for the US and its closest allies. For the British state, the retreat of its armed forces from Basra under cover of darkness, with their own record of torture and killings, was a humiliation.

There's little prospect, given the balance of power, of those most responsible for torture and atrocities in Iraq – let alone ordering the original aggression – of facing justice, or of the reparations Iraqis deserve. But there should be a greater chance of preventing more western military intervention in the Middle East, as Blair and his friends are now pressing for in Syria and Iran.

"Damn us for what we did," a British Iraq veteran wrote today. Far better would be to make it impossible for the politicians who sent them there to unleash such barbarism again.